1. Field of the Invention
The invention is directed to valves for controlling fluids, in which a valve closing member divides a low-pressure region in the valve from a high-pressure region. Such valves are known in the industry in various embodiments, for example in fuel injectors, especially common rail injectors, or in pumps of motor vehicles.
2. Description of the Prior Art
Such a valve is also known from European Patent Disclosure EP 0 477 400 A1; the valve described in this reference is actuatable via a piezoelectric actuator and has an arrangement for a travel converter, acting in the stroke direction, of the piezoelectric actuator. The deflection of the actuator is transmitted via a hydraulic chamber, which serves as a hydraulic booster and as a tolerance compensation element. The hydraulic chamber encloses a common work volume between two pistons defining the hydraulic chamber, of which one piston is embodied with a smaller diameter and is connected to a valve closing member to be triggered, and the other piston is embodied with a greater diameter and is connected to the piezoelectric actuator. The hydraulic chamber is fastened between the pistons in such a way that the actuating piston executes a stroke that is lengthened by the boosting ratio of the piston diameter, when the larger piston is moved by a certain travel distance by means of the piezoelectric actuator. In addition, via the work volume of the hydraulic chamber, tolerances, resulting for instance from different temperature expansion coefficients of the materials used and possible settling effects, can be compensated for without the valve closing member""s experiencing any change in its position.
To assure the function of such valves, the hydraulic system in the low-pressure region, in particular the hydraulic coupler, requires a system pressure. The system pressure drops because of leakage, unless hydraulic fluid is adequately replenished.
In common rail injectors known in the industry, for instance, in which the system pressure is expediently generated in the valve itself and is also kept as constant as possible upon a system start, the filling of the system pressure region is accomplished by the delivery of hydraulic fluid from the high-pressure region of the fuel to be controlled into the low-pressure region where the system pressure is to prevail. Often, the filling is done with the aid of leakage gaps, which are represented by leakage or filling pins. The system pressure is as a rule adjusted by means of a valve, and the system pressure can also be kept constant for a plurality of common rail valves, for example, as well.
However, if the system pressure in the hydraulic chamber is substantially constant, and is at least largely independent of the prevailing high pressure in the high-pressure region, this is problematic, since at high pressure values, great actuator force is required to open the valve closing member counter to the high-pressure direction; this dictates a correspondingly large, cost-intensive dimensioning of the actuator unit. Furthermore, at high pressure in the high-pressure region, the positive displacement of hydraulic volume out of the hydraulic chamber via the gaps surrounding the adjacent pistons is reinforced accordingly, meaning that under some circumstances, the refilling time for building up and maintaining the counterpressure on the low-pressure region is prolonged, so that for lack of complete refilling, in the event of a re-actuation of the valve soon thereafter, a shorter valve stroke will be executed, which can adversely affect the opening behavior of the entire valve.
The valve of the present invention for controlling fluids has the advantage that for refilling the hydraulic chamber, a system pressure dependent on the pressure level in the high-pressure region is furnished, and this system pressure assures the reliable function of the hydraulic chamber as a hydraulic booster. In a valve according to the invention, an increase in the system pressure is possible at a high pressure level in the high-pressure region in the hydraulic chamber, and as a result, the opening of the valve closing member counter to the high pressure applied is reinforced. In this way, compared to a valve with constant system pressure, a reduced triggering voltage of the actuator unit, preferably embodied as a piezoelectric unit, is sufficient. The valve according to the invention can therefore be equipped with a smaller and less-expensive actuator unit.
In addition, the invention makes a defined refilling of the low-pressure region, in particular the hydraulic chamber, possible. A very precise setting of the system pressure can be effected by flow changes at the throttle body, which are performed in an especially preferred way by hydroerosive rounding during assembly. The valve of the invention is thus distinguished not only by reliable furnishing of the requisite system pressure over the entire engine performance graph, but also by low costs for production and assembly. This is due above all to the structurally simple design of the valve, which makes it possible to define the variable system pressure in the hydraulic chamber by means of easily adjustable geometrical variables, such as the throttle flow and the dimensions of the body along which the system pressure is reduced to the low pressure.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.